Camera body:

Ergonomics, menu clarity
Weight, size, balance
Video and audio flexibility
Autofocus system
Features suited for the work I do
In-body image stabilization
Sensor technology
JPEG and video processor capabilities
Firmware history

Lenses:

Balance, weight, ergonomics
Sharpness, field flatness, freedom from flaws like chromatic aberration, distortion, and coma
Zoom range (if zoom)
In-lens image stabilization
Maximum aperture
Firmware history

...But beyond all that, and more important than any of that, is my willingness to learn to use it, and the photography knowledge, experience, viewpoints, attitudes, and foresights I bring to the gear.

Really not sure how to word this. If you do not have a preference for a particular camera brand and went shopping for a good system, would you consider a camera based on the following? Sensor, processor and/or lenses. Consider putting a mediocre lens on an excellent camera because of weight or cost? Buying a medium camera and putting excellent, expensive, weighty glass on it. I guess the question is, is the sensor, processor or lens the most important component? I do hope this is not the stupidest question you have heard.

My biggest issue with new glass isn't the glass, its the construction.

New stuff is almost always plastic and using tin solder. Both limit the useful lifespan of the product.

Older NIKKOR lenses, again no offense to other brands but these I am most familiar with, AF AFD and MF lenses can withstand amazing amounts of use and abuse.

If they don't have fungus or delimitation they will usually outlive the owner.

They also have a contact and color rendition, even in their lower level slower glass, that is seldom matched in modern lenses.

One of the best sports and wildlife primes ever made by anybody, IMHO the best, is the NIKKOR 180mm AF-D f2.8.

At twenty seven ounces and under 6 inches in length it is 63 ounces lighter and with a 52mm smaller diameter ... as well as being much shorter ... than a 300mm AFS-II f2.8, even though when mounted on an APS-C it offers an extremely close FOV as the 300 on a FF body.